In recent years, in a steam turbine plant to be used in a thermal power plant, a turbine bypass system is often employed. This turbine bypass system is installed, and thereby it is not necessary to decrease an amount of steam generated in a boiler even when a steam turbine is in a low-load region and is stopped. Therefore, it is possible to stabilize combustion of a boiler. Particularly, the turbine bypass system is effective for improving operational functions of starting up and stopping to be performed every day.
There is increased a steam turbine plant provided with a turbine bypass system, with an increase in a middle load thermal power plant. Such a turbine bypass system is provided with two-stage bypass systems of high pressure and low pressure.
FIG. 6 and FIG. 7 each are a system diagram of a steam turbine plant provided with a conventional turbine bypass system.
In the system of the steam turbine plant shown in FIG. 6, there is employed a start up method of circulating steam into a high-pressure turbine and an intermediate-pressure turbine simultaneously. In the system of the steam turbine plant shown in FIG. 7, there is employed a start up method of circulating steam only into an intermediate-pressure turbine. The difference between both the systems is whether or not a ventilator valve is installed between an exhaust hood of a high-pressure turbine and a condenser.
As shown in FIG. 6, steam generated in a superheater 411 of a boiler 410 flows into a high-pressure turbine 500 through a main steam stop valve 420 and a steam control valve 421. The steam exhausted from the high-pressure turbine 500 passes through a check valve 422 and is led to a reheater 412 in the boiler 410 to be reheated.
The steam that has passed through the reheater 412 is introduced into an intermediate-pressure turbine 510 through a reheat steam stop valve 423 and an intercept valve 424. The steam exhausted from the intermediate-pressure turbine 510 is led to a low-pressure turbine 520. A power generator 530 is coupled to a shaft end of the low-pressure turbine 520 and the power generator 530 is driven by the high-pressure turbine 500, the intermediate-pressure turbine 510, and the low-pressure turbine 520.
The steam exhausted from the low-pressure turbine 520 is led to a condenser 540 and is condensed to be condensed water. This condensed water is led to a low-pressure feed water heater 561 and a deaerator 562 by a condensate pump 550. Then, feed water that has passed through the deaerator 562 is pressurized by a feed water pump 551 and passes through a high-pressure feed water heater 563 to flow into the superheater 411 again.
In a pipe that branches off the middle of a pipe between the superheater 411 and the main steam stop valve 420, a high-pressure bypass valve 425 and an attemperator 570 are provided. This pipe is connected to the middle of a pipe provided between the check valve 422 and the boiler 410. Further, in the attemperator 570, a cooling water regulating valve 426 is installed in order to regulate an amount of cooling water to be supplied to the attemperator 570.
In a pipe that branches off the middle of a pipe between the reheater 412 and the reheat steam stop valve 423, a low-pressure bypass valve 427 and an attemperator 571 are provided. Further, in the attemperator 571, a cooling water regulating valve 428 is installed in order to regulate an amount of cooling water to be supplied to the attemperator 571.
Unlike the system shown in FIG. 6 above, in the system shown in FIG. 7, a pipe provided with a ventilator valve 580 is provided. This pipe branches off a pipe provided between a high-pressure turbine 500 and a check valve 422 and is connected to a condenser 540. Thereby, in the system shown in FIG. 7, the steam turbine plant operates so as to vacummize the inside of the high-pressure turbine 500 at the time of turbine start up.